1. Field of the Invention
The present invention relates to a region extraction technique for extracting a desired region from measured data.
2. Description of the Background Art
In recent years, a three-dimensional (3D) image (medical image) in a living body captured by an X-ray CT (Computed Tomography) system, an MRI (Magnetic Resonance Imaging) system or the like has been widely used in the medical field. Accordingly, information on organs and the like in the body can visually be identified, so that an improved diagnostic accuracy can be expected. On the other hand, however, a 3D image for use in diagnosis consists of several tens to several hundreds of slice images, which imposes a significant burden of acquiring only information necessary for diagnosis from such a huge amount of information on a diagnostician.
Therefore, with the growing demand for a computer-aided quantitative or automatic diagnosis, CAD (Computer-aided diagnosis) systems are under active study.
For conducting a computer-aided diagnosis, it is an important issue to precisely extract information necessary for diagnosis, that is, the region or shape, etc. of an organ.
As a technique for extracting an organ region, the model fitting technique of deforming a previously-prepared standard model on the basis of energy minimizing principles to find a target contour is proposed (Baigalmaa TSAGAAN, Akinobu SHIMIZU, Hidefumi KOBATAKE and Kunihisa MIYAKAWA: “Development of Extraction Method of Kidneys from Abdominal CT Images Using a Three Dimensional Deformable Model”, Trans. of IEICE in Japan, January 2002, D-II, Vol. J85-D-II, No. 1, pp. 140-148).
This technique deforms a previously-characterized model called a standard model to extract the region of concern, which allows highly accurate extraction.
However, the quality of extraction results using that technique depends upon the initial position of the standard model prior to the fitting process, which raises a great issue of how to locate the standard model in a position suitable for model fitting. In the aforementioned paper, for extraction of the kidney region, the initial position of the standard model is determined using the position of gravity center of kidney registered in a database. Accordingly, there is a problem in that it is difficult to obtain good extraction results when the position of gravity center of kidney in measured data (3D image) is displaced from the position of gravity center registered in the database.